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The drain on the battery by the RCM4510W is typically 7.5 µA when no other power is supplied.
If a 165 mA·h battery is used, the battery can last about 2.5 years:
165 mA·h
------------------------
7.5 µA
The actual battery life in your application will depend on the current drawn by components not on
the RCM4510W and on the storage capacity of the battery. The RCM4510W does not drain the bat-
tery while it is powered up normally.
Cycle the main power off/on after you install a backup battery for the first time, and whenever
you replace the battery. This step will minimize the current drawn by the real-time clock oscilla-
tor circuit from the backup battery should the RCM4510W experience a loss of main power.
NOTE: Remember to cycle the main power off/on any time the RCM4510W is removed from the
Prototyping Board or motherboard since that is where the backup battery would be located.
Rabbit's Technical Note TN235, External 32.768 kHz Oscillator Circuits, provides additional
information about the current draw by the real-time clock oscillator circuit.
C.1.2 Battery-Backup Circuit
Figure C-2 shows the battery-backup circuit.
The battery-backup circuit serves three purposes:
• It reduces the battery voltage to the SRAM and to the real-time clock, thereby limiting the cur-
rent consumed by the real-time clock and lengthening the battery life.
• It ensures that current can flow only out of the battery to prevent charging the battery.
• A voltage, VOSC, is supplied to U11, which keeps the 32.768 kHz oscillator working when
the voltage begins to drop.
C.1.3 Reset Generator
The RCM4510W uses a reset generator to reset the Rabbit 4000 microprocessor when the voltage
drops below the voltage necessary for reliable operation. The reset occurs between 2.85 V and 3.00
V, typically 2.93 V. Since the RCM4510W will operate at voltages as low as 3.0 V, exercise care
User's Manual
=
2.5 years.
External Battery
D4
VBAT-EXT
100 kW
Figure C-2. RCM4510W Backup Battery Circuit
VOSC
VRAM
R15
R14
47 kW
C45
10 nF
94
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